Biological assays for analyte detection generally involve attaching to the analyte (e.g., nucleic acids, proteins, hormones, lipids, or cells) a signal-generating moiety. Fluorescence-based bioassays require the detection of weak fluorescence signals. In a typical assay, the analyte is deposited onto a solid substrate such as a microscope slide or a glass chip. After undergoing biochemical treatment and fluorescent staining, the slide is examined with an optical instrument such as a fluorescence microscope. Light of certain wavelengths is applied to the slide, and the fluorescent emission from the deposited biomaterial is collected as a signal.
Transparent soda-lime and borosilicate glasses are commonly used as substrates to support fluorescently labeled samples. However, many of these materials exhibit significant autofluorescence, have finite absorbance, and can produce fluorescent emission throughout the visible region. A typical soda-lime glass slide can produce background fluorescence equivalent to a layer of a commonly used fluorescent dye with a surface density of more than 1.times.10.sup.9 fluorophors/cm.sup.2. This background fluorescence along with noise from other sources, such as stray light and Rayleigh and Raman scattering, can obscure the detection of weak fluorescent signals from the analyte, limiting the sensitivity of the assay.
Further, in many fluorescent assays for nucleic acid detection, nucleic acids are attached to a solid support via chemical linkers. Such linkers often are autofluorescent and can introduce background fluorescence.